Abstract: In the Dutch Field Margin Project a field study was carried out in 1990 and 1992 to investigate the extent to which unsprayed field margins offer scope for increasing butterfly abundance in agricultural areas. To this end the outer 3–6 m of fields of winter wheat or potatoes were left unsprayed with herbicides or insecticides. The number of butterflies in the unsprayed margins was compared with numbers in sprayed margins. Six species were found to be abundant: Maniola jurtina, Lasiommata megera, Coenonympha pamphilus, Pieris rapae, Pieris napi and Thymelicus lineola. In both years in the unsprayed winter wheat edges a significant increase was found in the number of species (≅ factor of 2.3) and the number of individuals (a factor of 4.6–4.9). In the unsprayed potato edges only in 1992 the increase in the number of species and individuals was significant (a factor of 3.6 and 6.9, respectively). Also at the level of crop edge plus adjacent field boundary (ditch bank and field edge), the number of species and individuals increased significantly in winter wheat in both years, and in potatoes in 1992 only. The ecological relevance of the results is discussed.